Lower your internal resolution(I use 1152x864, with our cards, however native gives best results). This game have some demanding graphics. My fps varies from 30 to 70, but most of the time is 50. I use all the available speedhacks for EE, IOP and VU with moderate VU cycle stealing.
Emu - PCSX2 r1329, Gsdx 1375 SPU - X 1.1